In one example of known light emitting apparatuses that use an LED chip, a resin layer (color conversion layer) containing phosphor particles is disposed around the LED chip. The phosphor in the color conversion layer is excited by absorbing part of the light emitted from the LED chip and emits fluorescent light. For example, the light emitting apparatus as disclosed in Japanese Patent Application Laid-Open No. 2005-109434 can be configured to include an LED chip that can emit blue light, and a phosphor that can emit yellowish orange fluorescent light that is complementary to the blue light. This light emitting apparatus can emit white light resulting from the mixture of the blue light from the LED chip with the yellowish orange fluorescent light from the phosphor.
To form the color conversion layer using a resin containing phosphor particles, a paste prepared by adding the phosphor particles to a resin material can be applied in drop form onto the LED chip, or a printing method such as stencil printing or screen printing can be used. Therefore, it is desirable to adjust the viscosity of the paste according to the method of forming that is used.
Japanese Translation of PCT International Application No. 2005-524737 discloses a light emitting diode element including a color conversion layer to which a thickener partly composed of nanoparticles is added. In this publication, the disclosed particle diameter of the thickener is 1 nm or more and 25 nm or less.
Japanese Patent Application Laid-Open No. 2007-19459 describes that optical properties and workability can be improved by adding inorganic oxide particles to a color conversion member containing a phosphor. For example, silica particles having a diameter of approximately 10 nm can exhibit a strong viscosity adjusting effect, and silica particles having a diameter of several μm can impart little thixotropy but exhibit the effect of suppressing cracks and shrinkage. Moreover, the addition of inorganic oxide particles having a diameter of approximately 1 μm can improve a scattering effect, and the addition of high-refractive index particles having a diameter of 3 to 5 nm can increase the refractive index. These particles may be used in combination.